US7493889B2 - Method for controlling the composition of a fuel/air mixture for an internal combustion engine - Google Patents

Method for controlling the composition of a fuel/air mixture for an internal combustion engine Download PDF

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Publication number
US7493889B2
US7493889B2 US11/836,996 US83699607A US7493889B2 US 7493889 B2 US7493889 B2 US 7493889B2 US 83699607 A US83699607 A US 83699607A US 7493889 B2 US7493889 B2 US 7493889B2
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Prior art keywords
fuel
engine speed
control
control circuit
valve
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US20080041338A1 (en
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Hans Nickel
Claus Naegele
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Andreas Stihl AG and Co KG
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Andreas Stihl AG and Co KG
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Assigned to ANDREAS STIHL AG & CO. KG reassignment ANDREAS STIHL AG & CO. KG ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NAEGELE, CLAUS, NICKEL, HANS
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/04—Introducing corrections for particular operating conditions
    • F02D41/08—Introducing corrections for particular operating conditions for idling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2400/00—Control systems adapted for specific engine types; Special features of engine control systems not otherwise provided for; Power supply, connectors or cabling for engine control systems
    • F02D2400/04—Two-stroke combustion engines with electronic control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2400/00—Control systems adapted for specific engine types; Special features of engine control systems not otherwise provided for; Power supply, connectors or cabling for engine control systems
    • F02D2400/06—Small engines with electronic control, e.g. for hand held tools
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
    • F02P5/00—Advancing or retarding ignition; Control therefor
    • F02P5/04—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions
    • F02P5/145—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions using electrical means
    • F02P5/15—Digital data processing
    • F02P5/1502—Digital data processing using one central computing unit
    • F02P5/1508—Digital data processing using one central computing unit with particular means during idling

Definitions

  • the invention relates to a method for controlling a composition of a fuel/air mixture supplied to an internal combustion engine, in particular, an internal combustion engine embodied as a two-stroke engine.
  • the internal combustion engine has a cylinder with a combustion chamber provided with a spark plug.
  • the combustion chamber is delimited by a piston driving a crankshaft.
  • An ignition control unit is connected to the spark plug and, depending on the rotary speed of the crankshaft, triggers at an adjusted ignition timing an ignition spark at the spark plug.
  • a speed control circuit maintains the actual rotary speed of the crankshaft within preset limits.
  • a controllable metering device is provided for at least one component of the fuel/air mixture.
  • Hand-held power tools such as motor chain saws, trimmers, blowers or similar devices are preferably driven by an internal combustion engine, for example, a two-stroke engine, that, when employing modern technology, is lively, powerful, and still can be operated in an environment-friendly way.
  • an internal combustion engine for example, a two-stroke engine
  • microprocessors are used for engine control that, depending on operating parameters, control ignition of the internal combustion engine.
  • the controller used in this connection is usually a so-called PI or PID controller, i.e., a controller with a proportional term and an integral term.
  • the engine speed is not only dependent on the ignition timing but also on the composition of the mixture.
  • the mixture can also be varied as a control variable, a control intervention in regard to the mixture composition, on the one hand, and in regard to ignition timing, on the other hand, in particular during idling, can cause the system to undershoot or overshoot the control range. If this is the case, the engine can stall or the idle speed can no longer be maintained.
  • this is achieved in that at a predeterminable point in time a disruptive variable is introduced and, immediately after introduction of the disruptive variable, the activity of the engine speed control circuit is monitored and evaluated. Depending on the result of the evaluation, at least one variable or a parameter having an effect on the operation of the internal combustion engine is adjusted; preferably, one of the components of the fuel/air mixture is adjusted.
  • Other operating parameters are also suitable as a variable, for example, ignition timing, compression rate or the like.
  • the engine speed as a command variable of the control circuit will try to adjust.
  • the engine speed control circuit however will immediately counteract in order to maintain the preset engine speed.
  • the engine speed control prevents an increase or drop of the engine speed by appropriate control intervention in the ignition.
  • This activity of the engine speed control circuit is mirrored in the control term and is monitored and evaluated in order to control, based on the result of evaluation, the metering device for the components of the mixture in such a way that one component of the mixture, depending on the result of the evaluation of the activity, is adjusted in order to obtain a mixture composition with an optimized air ratio ⁇ .
  • control term of the control circuit for example, the proportional term of the engine speed controller can be evaluated as a parameter for the control deviation and the control intervention to be carried out.
  • the proportional term of the control loop is thus a measure of the momentary ratio of fuel and air in the mixture.
  • a change of the fuel/air mixture is carried out wherein the fuel proportion and/or the mixture proportion can be changed.
  • the fuel amount is changed by means of the electromagnetically controlled valve (solenoid valve) in order to adjust, depending on the detected activity of the control loop, the composition of the fuel/air mixture in regard to an optimal air ratio ⁇ (lambda value).
  • This interaction between disruptive variable, control action, and change of the mixture proportions is done until an optimal value for the air ratio ⁇ is reached.
  • the parameter to be changed for adjusting ⁇ is the fuel quantity of the fuel/air mixture; however, it can also be advantageous to change the air quantity instead of the fuel quantity.
  • the valve is operated as a synchronized valve that expediently is open in the currentless state. Also, a linear valve or a proportional valve can be used that is to be controlled appropriately.
  • FIG. 1 is a schematic illustration of an internal combustion engine with intake part and schematically illustrated control circuit.
  • FIG. 2 is a schematic illustration of a basic circuit diagram of a carburetor arrangement with solenoid valve.
  • FIG. 3 is a flowchart illustrating schematically the method according to the invention.
  • FIG. 4 is a schematic illustration of an engine speed curve plotted against the air ratio ⁇ .
  • FIG. 5 is a schematic illustration of another carburetor arrangement with a solenoid valve for switching the idle jets.
  • FIG. 1 shows an internal combustion engine 1 that is a two-stroke engine in the illustrated embodiment.
  • the internal combustion engine can also be embodied as a four-stroke engine, a two-stroke engine with scavenging air or a similar engine.
  • the internal combustion engine 1 illustrated in FIG. 1 has a cylinder 2 with a reciprocating piston 3 that drives in rotation a crankshaft 5 supported in crankcase 4 .
  • the crankshaft 5 is connected by means of a connecting rod 6 to the piston 3 .
  • the piston 3 controls a mixture intake 10 that takes in combustion air through intake passage 11 and air filter 17 when underpressure is present within the crankcase 4 .
  • fuel is admixed to the incoming combustion air.
  • a fuel/air mixture is taken into the crankcase 4 and, as the piston moves downwardly, is conveyed through transfer passages 7 formed in the cylinder 2 into the combustion chamber 8 .
  • ignition control unit 13 an ignition spark is triggered at the spark plug 9 ; the spark ignites the fuel/air mixture compressed in the internal combustion chamber 8 by the upwardly moving piston 3 and, upon downward stroke of the piston 3 as a result of combustion, the crankshaft 5 is driven.
  • the combustion gases are exhausted by means of an exhaust port 18 that is preferably controlled by the piston 3 .
  • a wheel 14 is connected to the crankshaft 5 ; it can be a flywheel, a fan wheel or a similar wheel.
  • a magnet is arranged on the wheel 14 and induces a voltage in a coil 15 arranged stationarily relative to the circumference of the wheel 14 .
  • an engine speed sensor 16 is arranged that monitors the engine speed of the internal combustion engine.
  • the engine speed sensor 16 delivers a pulse sequence wherein for each revolution of the crankshaft 5 preferably several pulses are delivered.
  • the pulse sequence is supplied by signal line 19 to the ignition control unit 13 and processed therein, preferably by using a processor.
  • the voltage of the stationary coil 15 is supplied to the ignition control unit 13 that provides the ignition energy for the spark at the spark plug 9 . Moreover, by means of the induced voltage of the coil 15 a valve circuit 20 that is provided for controlling the solenoid valve 21 is operated also.
  • the valve 21 is provided in the fuel system 30 and serves for controlling the fuel supply. For this purpose, the solenoid valve 21 is connected by control line 22 to the valve circuit 20 .
  • the fuel supply into the intake passage 11 is adjustable. It can also be expedient to supply air instead of fuel through a solenoid valve. In the illustrated embodiment, the fuel amount of the mixture is changed for adjusting the mixture. A control for changing the air quantity of the mixture operates in the same way.
  • the fuel system 30 comprises a control chamber 23 of carburetor 12 as well as fuel tank 24 from where fuel is supplied to the control chamber via fuel line 25 .
  • a fuel pump 26 is arranged for this purpose.
  • the fuel pump 26 can be driven, for example, by the alternating crankcase pressure in the crankcase 4 of the internal combustion engine 1 .
  • the pressure side of the fuel pump 26 is connected by intake valve 27 to the control chamber 23 that is delimited by a diaphragm 28 .
  • the diaphragm 28 controls by means of control lever 29 the intake valve 27 against the force of a spring 29 a.
  • a fuel line 25 a is connected to the control chamber 23 and branches off to a main jet HD, expediently a partial load jet TD and several idle jets L 0 , L 1 , and L 2 opening into the intake passage 11 .
  • a switchable solenoid valve 21 in the fuel line 25 a between the control chamber 23 and the jets a switchable solenoid valve 21 is arranged that, as shown in FIG. 2 , is open preferably in the currentless state.
  • a spring 21 a is provided, for example, that force-loads the valve member 21 b into the open position.
  • a control coil of the solenoid valve 21 is to be supplied by valve control circuit 20 with supply voltage. When the supply voltage is supplied to the control coil of the valve 21 , the valve member 21 b is retracted against the force of the spring 21 a and fuel supply is blocked.
  • FIG. 2 shows in an exemplary fashion a signal sequence 50 that can be supplied via the control line 22 to the valve 21 .
  • the valve 21 over time t, is either switched on or off. At the time when a signal is present, the valve 21 is always switched off.
  • the valve is currentless and open.
  • the width of the individual signals 51 , 52 , and 53 is adjusted in accordance with preset values of the valve control circuit 20 so that the valve 21 is controlled by a pulse width modulated signal sequence 50 . It can also be expedient to configure the control pulses 51 , 52 , 53 to be of the same width and to supply a frequency-modulated signal sequence to the valve 21 . Also, the use of an appropriately controlled linear valve or proportional valve can be expedient.
  • the main jet path 31 Downstream of the valve 21 the main jet path 31 is provided that is connected by means of adjusting element 32 as well as a throttle 33 and a check valve 34 to the main jet HD in the area of the venturi section 35 of the intake passage 11 .
  • a partial load jet path 36 that supplies by means of a fixed throttle 37 and a check valve 37 a the partial load valve TD.
  • the partial load valve TD in the flow direction 38 is downstream of the venturi section 35 approximately at the level of the idle jet L 1 .
  • the jets are illustrated adjacent to one another for the purpose of simplifying the drawing.
  • a pivotable throttle valve 44 is positioned in the intake passage 11 .
  • the idle jets L 1 and L 2 open into the intake passage 11 and, downstream of the throttle valve 44 , the exit port L 0 is positioned. All ports L 0 , L 1 , L 2 are supplied by means of a common idle chamber 40 .
  • the idle jet L 1 is positioned approximately at the level of the axis 45 of the throttle valve 44 and is connected by throttle 42 to the idle chamber 40 .
  • the idle jet L 2 opens upstream of the idle jet L 1 into the intake passage 11 and is connected also by means of throttle 43 to the idle chamber 40 .
  • the idle chamber 40 is connected by idle adjusting screw 39 and preferably a check valve 39 a to the main jet path 31 .
  • the exit port L 0 opens downstream of the throttle valve 44 into the intake passage 11 and is connected by throttle 41 to the idle chamber 40 .
  • a choke 46 is arranged that, as is known in the art, is closed during cold start of the internal combustion engine in order to enrich the mixture.
  • the configuration of the fuel system 30 with solenoid valve 21 serves for providing a modified fuel supply in order to effect, independent of the vacuum in the intake passage 11 , the fuel quantity.
  • the valve control circuit 20 is provided that, through control line 48 , is supplied with control signals of the ignition control unit 13 .
  • the valve control illustrated in FIG. 3 comprises an engine speed control loop (circuit) 55 which is schematically illustrated by solid lines.
  • engine speed limits are set within which the engine speed is to be maintained by the control loop.
  • a lower engine speed n L and an upper engine speed n H are set so that, for example, at idle the engine speed control loop 55 maintains the engine speed of the internal combustion engine precisely between the lower engine speed n L and the upper engine speed n H .
  • an idle speed with a fluctuation width of 400/m can be preset.
  • a load switch 60 can be provided whose output signal is evaluated in a setting unit 61 and converted to appropriate engine speed limits. The load switch 60 recognizes idle and load situations.
  • the preset engine speed limits are compared in the comparators 62 and 63 with the actual engine speed n actual that is supplied by means of the engine speed sensor 16 .
  • the actual engine speed n actual is checked to see whether it is greater than the lower engine speed limit n L . If this is the case, the second comparator 63 is activated which checks whether the actual engine speed n actual is greater than the upper engine speed limit n H . Is this not the case, the loop is closed by means of branch 64 and another pass through the engine speed loop is carried out depending on the load state (idle/full load).
  • branch 65 is activated by means of which an intervention in the ignition control unit 13 can be done in such a way that the engine speed is increased.
  • the comparator 63 is connected to branch 66 when the actual engine speed n actual is greater than the upper engine speed limit n H .
  • a pass through branch 66 causes an intervention in the ignition control in such a way that the engine speed is lowered. In both branches 65 and 66 this is done by adjusting the ignition timing to “advanced” or “retarded” or, for the purpose of lowering the engine speed, also by suppressing ignition. Both branches 65 and 66 return to the start of the control loop as does branch 64 .
  • FIG. 4 shows the dependency of the engine speed n on the mixture composition (air ratio ⁇ ).
  • FIG. 4 shows clearly that for a mixture that is too lean the engine speed greatly increases and, in an extreme situation, can no longer be lowered by the engine speed control circuit 55 to the desired idle speed. The system is then outside of the control range.
  • FIG. 4 shows clearly that a mixture that is too rich leads to stalling of the internal combustion engine.
  • the engine speed control circuit 55 can no longer compensate the engine speed drop caused by the mixture being too rich; the engine will stall.
  • a disruptive variable ⁇ m s into the control loop, for example, by changing the mixture composition toward too rich or too lean, as is illustrated by dotted lines in the illustration of FIG. 3 .
  • the control can also be permanently active while in the other engine speed range it can operate stochastically.
  • the disruptive variable ⁇ m s is supplied in accordance with criteria of the ignition control at predetermined timing; this is realized by an appropriate control of the valve control circuit 20 . This can be done, for example, in that a signal 51 is made wider with regard to its pulse width for making the mixture more lean or is reduced with regard to its width for making the mixture richer.
  • any change of the mixture has direct effects on the engine speed n of the internal combustion engine.
  • the engine speed n will increase. This increase of the engine speed is suppressed by the control loop.
  • the internal combustion engine itself continues to operate substantially disruption-free wherein the engine speed branch 65 or 66 is used for compensation of the disruptive variable ⁇ m s .
  • the activity of the engine speed controller 55 is reflected in the control term of the control loop so that information can be provided in regard to an expected engine speed deviation, without intervention of the control circuit, by monitoring the control term, e.g. the proportional term or the integral term or even a derivative term.
  • the proportional term of the control loop is monitored by a detection device 70 and evaluated. It will calculate, based on the magnitude of the monitored control term, a required change of a proportion of the mixture and supply an appropriate control signal to the valve control circuit 20 in order to change the mixture proportion by a control variable plus or minus ⁇ m i .
  • the valve control circuit 20 changes in accordance with the obtained control command (control variable) the opening characteristics of the valve 21 ; this can be done by pulse width modulation or frequency modulation.
  • the proportion of the fuel in the mixture is thus changed so that the air ratio ⁇ for idle control is optimized, for example, and the engine speed is prevented from overshooting/undershooting the control range.
  • a disruptive variable is supplied again after elapse of a rest period and the work of the engine speed control circuit 55 is evaluated again by monitoring the control term that is necessary for controlling the engine speed change expected as a result of the disruptive variable ⁇ m s .
  • the overall arrangement is designed such that in the respective operating state an air ratio ⁇ is adjusted to be within the range of an optimum 69 shown in FIG. 4 .
  • the valve is provided in the main fuel supply line 25 a .
  • the preferably synchronized valve 21 is used for fuel supply into the idle system 40 , 41 , 42 , 43 .
  • the configuration of the fuel system in FIG. 5 is essentially identical to that of FIG. 2 so that same parts are referenced by same reference numerals.
  • an adjusting screw 39 b for controlling the fuel supply is provided in the main fuel supply path 25 a to the fuel system 30 a .
  • the control of the valve 21 is realized again by valve control circuit 20 that receives appropriate control signals from the ignition control unit 13 .
  • the arrangement according to the invention can be utilized in a simple way in connection with the control loop 55 of FIG. 3 or separate therefrom in order to adjust by appropriate control of the valve 21 the idle mixture with regard to its richness.
  • the load switch 60 indicates idle, the corresponding signal is processed and the valve control circuit 20 is controlled such that the richness of the mixture, i.e., the air ratio ⁇ (lambda value) is constant.
  • the mixture composition can be adjusted optimally wherein the engine speed itself is maintained exclusively by means of the ignition timing at the nominal value or within the preset nominal value limits.
  • the engine speed can also be adjusted by changing the richness of the mixture.
  • the control of the engine speed can also be realized by controlling the valve 21 and the adjustment of the proportions of fuel and air in the fuel/air mixture.
  • the valve 21 can be used in order to enrich the fuel/air mixture for improved acceleration.
  • the valve 21 can be controlled so as to provide a leaner mixture for avoiding the rich-come-down effect.
  • the arrangement according to FIG. 5 serves thus also for idle mixture control by means of the solenoid valve 21 .

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Electrical Control Of Ignition Timing (AREA)
US11/836,996 2006-08-16 2007-08-10 Method for controlling the composition of a fuel/air mixture for an internal combustion engine Active 2027-09-10 US7493889B2 (en)

Applications Claiming Priority (2)

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DE102006038277.3A DE102006038277B4 (de) 2006-08-16 2006-08-16 Verfahren zum Regeln der Zusammensetzung eines Kraftstoff/Luft-Gemisches für einen Verbrennungsmotor
DE102006038277.3 2006-08-16

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US7493889B2 true US7493889B2 (en) 2009-02-24

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090178648A1 (en) * 2008-01-11 2009-07-16 Andreas Stihl Ag & Co. Kg. Method for operating an internal combustion engine
US20110004395A1 (en) * 2009-07-04 2011-01-06 Andreas Stihl Ag & Co. Kg Method for Operating an Internal Combustion Engine
EP2787194A2 (en) 2013-04-05 2014-10-08 Yamabiko Corporation Internal combustion engine
US10648429B2 (en) 2010-07-01 2020-05-12 Husqvarna Ab Method for controlling the fuel supply to an internal combustion engine at start-up and a carburettor
US10704521B2 (en) 2016-01-15 2020-07-07 Suzhou Cleva Precision Machinery & Tchnology Co., Ltd. Portable gasoline tool and electronic ignition system thereof
US10851721B2 (en) 2016-01-15 2020-12-01 Suzhou Cleva Precision Machinery & Technology, Co., Ltd. Garden tool
US11242835B2 (en) 2015-09-15 2022-02-08 Andreas Stihl Ag & Co. Kg Method for operating a work apparatus having a combustion engine

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Publication number Priority date Publication date Assignee Title
DE102009031693A1 (de) * 2009-07-04 2011-01-05 Andreas Stihl Ag & Co. Kg Verfahren zum Betrieb eines Verbrennungsmotors
CN103392061B (zh) * 2011-02-23 2016-01-20 胡斯华纳有限公司 在切断速度下控制a/f比
JP2013151909A (ja) * 2012-01-25 2013-08-08 Iida Denki Kogyo Kk 手持ち式エンジン作業機の減速制御方法
DE102012002225A1 (de) * 2012-02-04 2013-08-08 Andreas Stihl Ag & Co. Kg "Handgeführtes Arbeitsgerät"
SE542396C2 (en) 2018-05-07 2020-04-21 Husqvarna Ab Improved fuel control

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US4979477A (en) * 1988-08-03 1990-12-25 Andreas Stihl Ignition circuit for a two-stroke engine
US5706783A (en) * 1995-08-25 1998-01-13 Yamaha Hatsudoki Kabushiki Kaisha Engine control arrangement
US5738073A (en) * 1995-11-08 1998-04-14 Sanshin Kogyo Kabushiki Kaisha Engine operation control system
US5775297A (en) * 1995-11-08 1998-07-07 Sanshin Kogyo Kabushiki Kaisha Engine operation control system
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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090178648A1 (en) * 2008-01-11 2009-07-16 Andreas Stihl Ag & Co. Kg. Method for operating an internal combustion engine
US8322326B2 (en) * 2008-01-11 2012-12-04 Andreas Stihl Ag & Co. Kg Method for operating an internal combustion engine
US20110004395A1 (en) * 2009-07-04 2011-01-06 Andreas Stihl Ag & Co. Kg Method for Operating an Internal Combustion Engine
US8914219B2 (en) 2009-07-04 2014-12-16 Andreas Stihl Ag & Co. Kg Method for operating an internal combustion engine
US10648429B2 (en) 2010-07-01 2020-05-12 Husqvarna Ab Method for controlling the fuel supply to an internal combustion engine at start-up and a carburettor
EP2787194A2 (en) 2013-04-05 2014-10-08 Yamabiko Corporation Internal combustion engine
US11242835B2 (en) 2015-09-15 2022-02-08 Andreas Stihl Ag & Co. Kg Method for operating a work apparatus having a combustion engine
US10704521B2 (en) 2016-01-15 2020-07-07 Suzhou Cleva Precision Machinery & Tchnology Co., Ltd. Portable gasoline tool and electronic ignition system thereof
US10851721B2 (en) 2016-01-15 2020-12-01 Suzhou Cleva Precision Machinery & Technology, Co., Ltd. Garden tool

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JP2008045545A (ja) 2008-02-28
CN101126356A (zh) 2008-02-20
DE102006038277A1 (de) 2008-02-21
CN101126356B (zh) 2012-11-14
DE102006038277B4 (de) 2021-01-21
US20080041338A1 (en) 2008-02-21

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